Public Tools Developed by USACE -- Climate-Impacted Hydrology

Managing hydrologic extremes due to climate variability is an essential mission of water management agencies. Climate change requires water resources managers to move from an equilibrium—or stationary—paradigm to one of constant evolution that recognizes the dynamic nature of physical and socioeconomic processes.

USACE infrastructure, operations, safety and maintenance programs are facing growing stresses caused by aging infrastructure, hydrologic nonstationarity, urban growth, coastal development, evolving navigation and shipping practices, changing agricultural practices, and increasing recognition of the need for ecosystem restoration. USACE must ensure that its systems and projects will remain adaptable and sustainable over time even if the frequency and severity of extreme hydrologic events may change.

Hydrological tools and methods supporting climate change adaptation planning and implementation, as discussed on the Hydrology to Support Adaptation page, is a major focus of Brekke et al. (2009) and subsequent discussions by the interagency Climate Change and Water Working Group (USACE 2011). The team is developing processes, methods and guidance for hydrology used in climate change impact assessments and adaptation planning and design.

Nonstationarity Detection Tool

Stationarity, or the assumption that the statistical characteristics of hydrologic time series data are constant through time, enables the use of well-accepted statistical methods in water resources planning and design in which future conditions rely primarily on the observed record. However, recent scientific evidence shows that—in some places, and for some impacts relevant to the operations of the U.S. Army Corps of Engineers (USACE)—climate change and human modifications of the watersheds are undermining this fundamental assumption, resulting in nonstationarity.

The Detection Tool enables the user to apply a series of statistical tests to assess the stationarity of annual instantaneous peak streamflow data series at any United States Geological Survey (USGS) streamflow gage site with more than 30 years of annual instantaneous peak streamflow records through Water Year 2014. The tool aids practitioners in identifying continuous periods of statistically homogenous (stationary) annual instantaneous peak streamflow datasets that can be adopted for further hydrologic analysis. The tool also allows users to conduct monotonic trend analyses on the identified subsets of stationary flow records. The tool facilitates access to USGS annual instantaneous peak streamflow records; does not require the user to have either specialized software or a background in advanced statistical analysis; provides consistent, repeatable analytical results that support peer review processes; and allows for consistent updates over time. USACE technical guidance on the detection of nonstationarities in annual maximum flows is contained in Engineer Technical Letter 1100-2-3.

The User Manual includes a discussion of the technical concepts incorporated into the Nonstationarity Detection Tool, a description of the user interface, an explanation of how to apply the user interface to execute hydrologic analysis, and a series of examples highlighting how the tool is applied. This user guide does not cover all possible situations one may encounter using the tool. The first step in conducting nonstationarity detection is to carry out data preparation and exploratory data analysis, which are described in detail in Section 3. The Nonstationarity Detection Tool is not a substitute for professional engineering judgment. For more information about the tool, you can read the fact sheet. You can also watch a video(mp4, 54.1 MB) that explains how to use the tool.

ECB 2016-25, released on 16 Sept 2016, supersedes and updates ECB 2014-10. The qualitative analysis required by this ECB includes consideration of both past (observed) changes as well as potential future (projected) changes to relevant hydrologic inputs as part of a first-order statistical analysis of the potential impacts to particular hydrologic elements of the study. This analysis can be very useful in considering future without project conditions (FWOP) and the potential direction of climate change. Examples of this type of analysis is provided in Appendix C.

The Climate Hydrology Assessment Tool allows users to easily access both existing and projected climate data to develop repeatable analytical results using consistent information: reducing potential error and increasing the development of information so that it can be used earlier in the decision-making process, ideally in the development of risk registers. This tool steps user through the process of developing information and supplies graphics suitable for use in a report including: trend detection in observed annual maximum daily flow, trend detection in observed annual maximum 3-day flow, climate-modeled annual maximum monthly flow range, and trend detection in annual maximum monthly flow models.

Indicators for Vulnerability Assessments

Vulnerability assessments are necessary to understand when and how changing conditions impact the performance, function, and reliability of our projects and programs. USACE has completed several activities associated with high level assessments of vulnerability to climate change. These include a preliminary assessment presented in USGS Circular 1331 and a high-level vulnerability analysis to climate change required by the Council on Environmental Quality. We are currently assessing vulnerability using a nationwide screening-level tool that is based on indicators related to hazard, exposure, and sensitivity.

These indicators and their current use are described in a series of indicator fact sheets. These indicators will be updated periodically.

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